1. Field of the Invention
The present invention relates to a method for controlling information recording, and more particularly to a method for controlling information recording suitable for a erasable optical disk system.
2. Description of the Prior Art
In a prior art optical disk, information is recorded by forming small pits by irradiating a laser beam to a record film. Accordingly, once information is recorded, the information cannot be updated. As shown in Japanese Patent Unexamined Publication No. 59-165207, if a defect block is detected when information is recorded, the information for that block is recorded in an alternative area.
In a prior art magnetic disk apparatus, an alternative area is assigned to a defect area and a pointer to the alternative area is written in the defect area. Thus, when the defect area is accessed, the alternative area is pointed to by the pointer.
Recently, a erasable optical disk has been developed and writing of information into the optical disk and updating thereof are attainable. However, if a defect block is detected when the information is recorded, the information to be written into that defective block is written into an alternative block. The defect block is created by a permanent defect of the block as well as temporary defect in which recording is not correctly done, e.g., by deposition of dust. A percentage of the latter block detect is relatively high. In the optical disk, the defect block can be detected by reading data after it has been written in order to check whether the data has been correctly written. Even if it is a temporary defect due to the deposition of dust, it is detected as an error in recording in the same manner as the permanent defect. Once a block is detected to be defective, the data is recorded in an alternative region and no data is subsequently written into the defect area. As a result, the number of blocks in the alternative area increases, and a block which has been temporarily determined to be defective but can now correctly record the data is not used. Thus, the number of blocks in the alternative area increases monotonously every time the data is written.